| Description |
I will present the results of magnetic, dielectric and magnetoelectric measurements on the spin-chain systems, belonging to Haldane spin-chain family, R2BaNiO5 (R=Tb, Sm), and a Li-based oxide, Li2Ni2Mo3O12.
Tb2BaNiO5exhibits antiferromagnetic transition around (TN=)64 K and another magnetic transition at 25 K, but ferroelectric transition is found at the lower magnetic transition temperature, unlike in many other heavy rare-earth members. In addition,we have found largest magneto-dielectric effect (around 18%), within the R2BaNiO5 family. In Sm2BaNiO5, which orders antiferromagnetic around 55 K, we find ferroelectric transition around 22 K. Implications of these findings (that is, bringing out the role of crystal-field effect on magnetoelectric coupling) will be discussed.
In the compound Li2Ni2Mo3O12, which consists of distortedhoneycomb and linear chain of Ni2+, we found relaxor ferroelectric behaviour around 200 K. Additionally, the intrinsic magneto-dielectric effect has been observed in a broad temperature range including room temperature for this compound.
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